A minimum gas fuel supply pressure is required to provide the motive force for the fuel to overcome losses due to strainers, valves, piping and fuel nozzles, and enter the combustion chamber of a gas turbine under all potential operating conditions.
The existing gas fuel control system is based on a fixed gas fuel supply pressure requirement (referred to as P2 pressure requirement) from full speed no load (FSNL) to base load, irrespective of ambient conditions. The fixed requirement is based on worst-case conditions: base load on the coldest day, that is the coldest ambient design temperature for the particular site. If the gas fuel supply pressure is less then the control system pressure requirement, the gas turbine is inhibited from starting. If the gas fuel supply pressure falls below the control system requirement by 20 psi during operation, the control system initiates a runback to a predetermined low load mode of operation and operator action is then required.
If source gas supply pressure is expected to be lower than the fixed gas turbine supply requirement, then expensive gas fuel compressors are required to ensure gas turbine operability. This, however, is a very expensive solution that costs plant owners millions of dollars in initial investment and consumes high auxiliary power loads. Indeed, the gas compressors pressurize the gas fuel to the cold ambient day supply pressure requirement even when the actual pressure required may be much lower, thereby wasting hundreds of kilowatts.